GB2619964A

GB2619964A - Method for detection of a bearing condition of a vacuum pump

Info

Publication number: GB2619964A
Application number: GB2209262.1A
Authority: GB
Inventors: Lucchetta Emiliano; Cobbett Andrew; Glyn Horler Richard
Original assignee: Edwards Ltd
Current assignee: Edwards Ltd
Priority date: 2022-06-24
Filing date: 2022-06-24
Publication date: 2023-12-27
Also published as: WO2023247926A1; GB202209262D0

Abstract

A method for detection of a bearing condition of a vacuum pump comprises detection of a bearing temperature of a bearing 32, detection of at least one second temperature of the vacuum pump, and determining a bearing condition based on the bearing temperature and the second temperature. The second temperature may be a rotor temperature, a stator temperature or an ambient temperature. The bearing condition may be determined from a change rate of the bearing temperature and/or second temperature, or from a difference between the bearing temperature and the second temperature, and may involve a predetermined look-up table or a correlation algorithm or correlation function. Determining the bearing condition may involve detecting a power consumption, rotational speed or acceleration rate of the pump. A vacuum pump comprises a first temperature sensor 22 to detect the temperature of a roller bearing 32 and a second temperature sensor 24.

Description

METHOD FOR DETECTION OF A BEARING CONDITION OF A VACUUM

PUMP

The present invention relates to a method for bearing condition detection of a vacuum pump and such a vacuum pump.

Common vacuum pumps comprise a housing and a rotor assembly rotatably disposed in the housing and supported by bearings such as roller bearings and/or magnetic bearings. The rotor assembly is rotated by an electromotor, and it comprises at least one rotor element interacting with at least one stator element, in order to convey a gaseous medium from an inlet of the vacuum pump towards an outlet of the vacuum pump. Therein, in particular for turbo-molecular pumps, high rotational speeds are used in order to provide a pump effect and a sufficient pump performance of the vacuum pump. Due to the high rotational speeds of the rotor assembly, failures can be very destructive and create damage and costs. In particular mechanical bearings such as roller bearing are one of the main components that can wear and result in a product failure. Thus, methods of detecting failure of the bearings are therefore necessary to predict the bearing conditions and prevent damages and related costs by shutting down the vacuum pump before damage to the customer systems occurs or provide a warning which enables the engineers to replace/fix the problem, i. e. replace the mechanical bearings, with minimal disruption of the customers system.

Various different approaches for detecting bearing failure are known. Thereby noise sensors can be implemented, detecting the noise of the bearing in order to predict by a change of frequencies a failure of the roller bearing. Alternatively, bearing temperature is measured providing an indication of the bearing condition. However, local temperature detection on the bearing can indicate that a fault has occurred wherein false failures could be generated if the product is naturally being heated while the application or by other/external factors. Also -2 -other techniques to detect bearing failures may lead to detection of false failures.

Thus, it is an object of the present invention to provide a method for reliably predicting bearing conditions and preventing bearing failure.

The problem is solved by a method according to claim 1 and a vacuum pump according to claim 14.

The method for detection of a bearing condition of a vacuum pump according to the present invention comprises the steps: Detection of the bearing temperature of the bearing of the vacuum pump; Detection of at least one second temperature of the vacuum pump; and Determining a bearing condition on the basis of the bearing temperature and the second temperature.

In a first step the bearing temperature of the bearing of the vacuum pump is detected, wherein the bearing is the bearing to be monitored and for which the bearing condition shall be determined. In a second step a second temperature of the vacuum pump is detected, wherein the second temperature is in particular one or more of a rotor temperature, a stator temperature and an ambient temperature of the vacuum pump or a combination thereof. From the detected bearing temperature and the detected second temperature a bearing condition is determined. Thus, the bearing temperature and the second temperature are used in combination to predict or determine the bearing condition. By considering the second temperature of the vacuum pump, false failure detections can be prevented and a more reliable detection of bearing failure can be implemented. Therein, by the present invention a simple method is provided in order to reliably predict the bearing condition. In particular, measurement of temperatures is simple and reliable, thereby also increasing the reliability of the determined bearing condition. Further temperature sensors are cheap and small and thus can easily be implemented in vacuum pumps of any kind. -3 -

Preferably, no threshold is defined for the absolute values of the bearing temperature and preferably no threshold is defined for the absolute values of the second temperature. Such threshold for the absolute value of the bearing temperature or the absolute value of the second temperature would correspond to the current solution of the prior art with the respective disadvantages mentioned above, i.e. producing false failure detections.

Preferably the bearing to be monitored which temperature is detected as bearing temperature is a mechanical bearing or roller bearing.

Preferably, the bearing temperature is measured contact free. Thus, no temperature sensor needs to be directly attached to the bearing. Contact free measurement of the bearing temperature can be performed for example optically or by detecting radiated heat. Alternatively, the bearing temperature can be detected directly in contact with the bearing such that a bearing temperature sensor is directly attached to a part of the bearing or is placed in close proximity to the bearing to be monitored. However, the present invention is not limited to the specific method for detecting the bearing temperature.

Preferably, from the bearing temperature and/or the second temperature a change rate is determined, wherein the bearing condition is determined on the basis of the change rate of the respective temperature. Therein, the change rate may be related to the first derivative of the bearing temperature or the second temperature over time or the like. The change rate of the bearing temperature and/or the change rate of the second temperature can be used in addition to the absolute values for the bearing temperature and/or the second temperature or can be used instead in order to determine the bearing condition of the bearing to be monitored.

Preferably, in addition to the bearing temperature and the second temperature, further an operation parameter is detected and considered when determining -4 -the bearing condition. Therein, in particular the operation parameter includes one or more of a power consumption of the vacuum pump, i. e. the electrical motor, a rotational speed of the rotor assembly or an acceleration rate of the rotor assembly of the vacuum pump. Thus, by including further operation parameters in addition to the bearing temperature and the second temperature, reliability of the prediction of the bearing condition can be further increased.

Preferably, determining a bearing condition on the basis of the bearing temperature and the second temperature includes determining the difference between the bearing temperature and the second temperature. Therein, the bearing condition is determined on the basis of the difference between the bearing temperature and the second temperature. In particular, the bearing condition can be determined on the basis of a change rate of the difference between the bearing temperature and the second temperature. The change rate may be related to the first derivative of the difference between the bearing temperature and the second temperature over time or the like. Therein, the difference between the bearing temperature and the second temperature and/or the change rate of the difference can be used in addition to the absolute values of the bearing temperature and the second temperature or instead.

Preferably, the difference between the bearing temperature and the second temperature and/or the change rate of the difference between the bearing temperature and the second temperature is compared with a preset threshold, wherein determining the bearing condition is based on this comparison. In particular, if the difference or the change rate of the difference are above the preset threshold, a bearing failure is detected. Alternatively, if the difference and the change rate of the difference are above the preset threshold, a bearing failure is detected. Alternatively, if only one of the difference or the change rate of the difference are above the preset threshold, a bearing failure is detected. Therein, for detecting a bearing failure, the comparison of the difference between the bearing temperature and the second temperature and/or the change rate of the -5 -difference between the bearing temperature and the second temperature can be combined with comparison of other operational parameters with a respective threshold and/or the comparison of any absolute value of the bearing temperature and the second temperature with a respective threshold and/or the comparison of the change rate of the bearing temperature with a respective threshold and/or the comparison of the change rate of the second temperature with a respective threshold. Therein, the respective thresholds can be set individually to the respective parameter or a common threshold can be set for all used parameters together.

Preferably, the preset threshold is altered if the rotational speed changes or has changed with in a preset period of time. The rotational speed change can take place quickly (e.g. less than 2 to 10 minutes for 0 rpm to max speed), whereas the temperature or temperature difference will evolve more slowly so that the preset threshold would be exceeded when the speed has reached the desired value. Thus, occurrence of a change of rotational speed is considered with in the preset period of time. Therein, the preset period of time relates to the time necessary for the vacuum pump to heat up when started or reach a setpoint when changing the load. Usually, the preset time period is between 5 and 60min, more preferably, between 5 and 30min and most preferably between 5 and 10min.

Preferably, determining a bearing condition on the basis of the bearing temperature and the second temperature includes: providing a predetermined look-up table to indicate the bearing condition in dependence on the bearing temperature and the second temperature. Therein, in particular the look-up table is predetermined for a specific vacuum pump type and/or specific application of a vacuum pump and provides a direct link between bearing condition of bearing failure and the measured bearing temperature and the second temperature or a calculated value from the bearing temperature and the second temperature, such as the change rate of one or more of these temperatures or the difference -6 -between these temperatures or the change rate of the difference. In addition, the look-up table may also contain other parameters such as operation parameters mentioned above.

Preferably, determining a bearing condition on the basis of the bearing temperature and the second temperature includes providing a correlation algorithm or correlation function, wherein by the correlation algorithm or correlation function the bearing temperature and the second temperature are correlated with the bearing condition. Therein the correlation algorithm may be a trained learning algorithm which is trained to correlate the bearing temperature and the second temperature to the respective bearing condition or bearing failure. Thus, over time, the correlation algorithm may be further trained to increase accuracy of detecting. Alternatively to a correlation algorithm, a functional relationship between the bearing temperature, the second temperature and the bearing condition can be used in order to indicate the bearing condition or the bearing failure.

Preferably, the bearing condition is provided by a bearing condition value, wherein the bearing condition value is determined on the basis of the bearing temperature and the second temperature. If the bearing condition value is above a bearing failure threshold, a bearing failure has occurred, and a warning signal is generated and/or the vacuum pump is shut down. Therein, the bearing condition value might be determined by the correlation algorithm or can be calculated by the correlation function. Alternatively, the bearing condition value is provided by the look-up table.

Preferably, the bearing failure threshold is altered if the rotational speed changes or has changed with in a preset period of time. The rotational speed change can take place quickly (e.g. less than 2 to 10 minutes for 0 rpm to max speed), whereas the temperature or temperature difference will evolve more slowly so that the bearing failure threshold would be exceeded when the speed -7 -has reached the desired value. Thus, occurrence of a change of rotational speed is considered with in the preset period of time. Therein, the preset period of time relates to the time necessary for the vacuum pump to heat up when started or reach a setpoint when changing the load. Usually, the preset time period is between 5 and 60min, more preferably, between 5 and 30min and most preferably between 5 and 10min.

Preferably, the bearing failure is determined when the bearing temperature increases while the second temperature is substantially constant. Therein "substantially constant" means that the change of the second temperature is smaller than the increase of the bearing temperature. In this case it can be concluded that a bearing failure occurred. In particular, if the rotational speed is constant, it is possible that a bearing failure may have occurred. Similarly an increase in power or fluctuations in power could provide further evidence of a failure.

Preferably no bearing failure is determined when the bearing temperature increases while the second temperature also increases, wherein the increase of the bearing temperature is larger than the increase of the second temperature if this occurs during start-up of the vacuum pump. The bearing temperature rapidly increases to operational temperature while, due to the thermal mass of the rotor assembly, the rotor temperature as second temperature increases slowly. Thus, despite an increase of the bearing temperature, no bearing failure is detected. In particular, if the rotational speed of the rotor increases or has recently increased within a preset period of time, a bearing failure can be reliably ruled out and false failure detection can be prevented.

Preferably no bearing failure is determined when the bearing temperature is substantially constant while the second temperature increases. This situation usually occurs during load of the vacuum pump. Therein "substantially constant" means that the change of the bearing temperature is smaller than the increase of the second temperature. The bearing temperature stays constant or almost -8 -constant while, due to the applied load to the vacuum pump, the rotor temperature as second temperature increases. Due to thermal separation of the rotor assembly and the bearings, heat is only slowly transferred to the bearing, thereby slowly increasing the bearing temperature. Thus, despite an increase of the bearing temperature, no bearing failure is detected. In particular, if the rotational speed of the rotor constant or almost constant, a bearing failure can be reliably ruled out and false failure detection can be prevented.

In another aspect the present invention relates to a vacuum pump comprising a housing, a rotor assembly disposed in the housing and rotatably supported by two bearings. Therein the rotor assembly includes at least one rotor element interacting with at least one stator element attached to the housing in order to convey a gaseous medium from an inlet of the vacuum pump to an outlet of the vacuum pump. Therein, at least on bearing is built as a mechanical bearing or roller bearing. A first temperature sensor is arranged at the at least one roller bearing to be monitored to detect a bearing temperature. A second temperature sensor is arranged at the vacuum pump in order to detect a second temperature. The first temperature sensor and the second temperature sensor are connected to a control unit, wherein the control unit is configured to perform the steps of the method described above. Therein, the control unit may be integrally formed with the main pump control. Alternatively, the control unit may be a separate module or unit. The separate module or unit can be directly attached to the vacuum pump itself or arranged separate and remotely from the vacuum pump, wherein the vacuum pump and the control unit are connected with each other to perform the steps of the method. Therein, connection can be provided via electrical/wired connection or wireless connection such as WLAN, Bluetooth, or any cellular network.

In the following the present invention is described in detail with reference to the accompanying figures. -9 -

The figures show: Figure 1 an embodiment of the vacuum pump according to the present invention, Figure 2 a flow diagram of the method according to the present invention, Figure 3 a first example according to the present invention, Figure 4 a second example according to the present invention and Figure 5 a third example according to the present invention.

Referring to Figure 1 showing a vacuum pump built as turbomolecular pump. The vacuum pump comprises a housing 10 including an inlet 12 and an outlet 14. A rotor shaft 16 is disposed in the housing and supported by a first bearing 18 built as permanent magnetic bearing in the example of Figure 1, and a second bearing 20, built as mechanical ball bearing 32.

Further, the first bearing 18 may comprise emergency running bearings 30 built as ball bearings. The rotor shaft 16 is driven by electromotor 31. Attached to the rotor shaft 16 are a plurality of pump elements built as rotor disks 34 interacting with stator elements 36 connected to the housing 10 of the vacuum pump and arranged alternating with the rotor disks 34. In addition, the vacuum pump of figure 1 comprises a Holweck stage 38 comprising a rotating cylinder 40 interacting with a threaded stator 42 connected to the housing. By rotating of the rotor shaft 16 a gaseous medium is conveyed from the inlet 12 of the vacuum pump towards the outlet 14. Although Figure 1 shows a turbomolecular vacuum pump, the present invention is not limited to a specific type of vacuum pump and the present invention can also be implemented into other vacuum pumps, -10 -and in particular molecular drag pumps. Further, the first bearing 18 could also be built as mechanical bearing, instead to the second bearing 20 or in addition.

As shown in Figure 1 a first temperature sensor 22 is placed in close proximity to the bearing 32 in order to detect the bearing temperature. Further, a second temperature sensor 24 is attached to the rotor 16. The first temperature sensor 22 and the second temperature sensor 24 are connected to a control unit (not shown) wherein the control unit is adapted to carry out the steps of the method according to the present invention and further elucidated with reference to Figure 2. There, the second temperature sensor 24 is in the example of Figure 1 attached to the rotor directly. However, other possibilities of detecting the rotor temperature as second temperature are also encompassed by the present invention and the present invention is not limited to a specific way how to detect the rotor temperature. For example, the second temperature sensor would not be attached directly to the rotor but would be non-contacting and held in the static part of the pump. The second temperature sensor would then measure the temp via Infra-Red or the radiated heat. Additionally or alternatively to the rotor temperature, other second temperatures could be detected, i.e. the ambient temperature and/or the stator temperature.

Referring to Figure 2 showing a flow diagram of the method according to the present invention to detect a bearing condition of a bearing of a vacuum pump in particular according to figure 1.

In step 501, a bearing temperature of the bearing of the vacuum pump is detected.

In step 502, at least one second temperature of the vacuum pump is detected. In step 503, a bearing condition is determined on the basis of the bearing temperature and the second temperature.

Thus, in step 501 by a first temperature sensor 22 a bearing temperature is detected from the bearing 32 to be monitored and which condition shall be determined. In step SO2 by the second temperature sensor 24 a second temperature is detected. Therein, the second temperature might be the temperature of the stator 36 of the vacuum pump or the ambient temperature of the vacuum pump. Preferably the second temperature is the rotor temperature. In step 503, on the basis of the bearing temperature and the second temperature, a bearing condition is determined. Therein false failure detections can be prevented by considering more than just the bearing temperature itself. In particular, no threshold is defined for the bearing temperature. Only by comparison or considering the bearing temperature together with the second temperature, the bearing condition of the bearing to be monitored can be reliably determined. Thus, bearing failures can be detected while a change of the operational state of the vacuum pump -also leading to change of temperature within the vacuum pump -will minimizes the risk of false failure detections.

Measurement of the bearing temperature alone will create false failure detections. Use of multiple measurements in combination will improve effectiveness and reliability of the prediction. In the scenarios shown in Figures 3 to 4, both rotor temperature and bearing temperature are monitored.

Referring to Figure 3, if the bearing is failing bearing temperature (line 50) is rising and there is a large increase in the bearing temperature. This may be a sudden spike or a steep but steady incline. Due to the relatively large thermal mass of the rotor and low thermal mass of the bearing, a large temperature rise in the bearing may only contribute a small temperature change in the rotor (line 52). So, by measuring both parts and detecting their relative temperature changes a bearing fault could be distinguished. However, during operation of the vacuum pump, the rotational speed (line 54) may be constant or slightly decreasing during bearing failure.

Referring to Figure 4, on start-up, the rotational speed (line 64) is increasing. The rotating elements of the bearing are being accelerated, frictional loads may -12 -be higher than normal since the running bands of the bearing may not be fully lubricated. Oil will start to fill into the bearing that is thicker than normal (as the pump may be cool), lots of power is being pumped into the motor to accelerate the pump. All this creates a rapid rise in bearing temperature (line 60). The rotor takes longer to heat as shown in Figure 4 (line 62), but warms at a greater rate than during a failure and with a different profile to the bearing fault as shown in Figure 3. To help understand temperature rise during start-up, rotor speed may be monitored as the rate of temperature rise in the rotor/bearing can then be linked to the change in speed of the pump or the recent change or speed of the pump within a preset period of time. If a large rise in bearing temperature is usually seen at this point, the bearing alarm threshold could be paused or altered as the rotational speed was changing. If the bearing fails whilst the pump speed is changing, then the rate of acceleration would be lower than normal as extra power would be needed to run the pump with a damaged bearing. Bearing temperature would also increase faster than normal due to localised frictional heating. Thus, by detecting the change rate of the bearing temperature, bearing failure could be reliably detected.

Referring Figure 5, with application loading, the rotor would likely see a temperature rise (line 72) change first then the bearing temperature (line 70) will follow. Thus, both the rotor and bearing temperature would increase together and the profile of change in the two parts would be different to a bearing failure, enabling the two to be determined and the risk of a false failure detection is reduced. Therein, the rotational speed (line 74) may remain almost constant.

If the temperature rise were due to other external factors, e.g an external magnetic field or ambient changes, the temperature profile would again be different which could be distinguished by observing the bearing temperature and at least one additional second temperature.

-13 -In all the examples shown, if a simple temperature threshold was used to determine whether a bearing failure is occurring, all options could have resulted in a fail being detected. However, through use of the rotor temperature in combination and the temperature changes on the two parts are observed the different modes can be determined and the risk of false failure detections reduced.

-14 -List of References: housing 12 inlet 14 outlet 16 rotor shaft 18 first bearing second bearing 22 first temperature sensor 24 second temperature sensor emergency running bearings 31 electromotor 32 ball bearing 34 rotor disks 36 stator elements 38 Holweck stage cylinder 42 threaded stator line 52 line 54 line line 62 line 64 line line 72 line 74 line

Claims

-15 -CLAIMS1. Method for detection of a bearing condition of a vacuum pump, comprising: Detection of a bearing temperature of the bearing of the vacuum pump; Detection of at least one second temperature of the vacuum pump; and Determining a bearing condition on the basis of the bearing temperature and the second temperature.
2. Method according to claim 1, wherein the second temperature is a rotor temperature and/or a stator temperature and/or ambient temperature of the vacuum pump.
3. Method according to claim 1 or 2, wherein the bearing temperature is measured contact free or directly in contact with the bearing.
4. Method according to any of claims 1 to 3, wherein from the bearing tem-perature and/or the second temperature a change rate is determined wherein the bearing condition is determined on the basis of the change rate.
5. Method according to any of claims 1 to 4, wherein determining a bearing condition on the basis of the bearing temperature and the second temperature includes: determining the difference between the bearing temperature and the second temperature to determine the bearing condition and/or a change rate of a difference between the bearing temperature and the second temperature to determine the bearing condition.
-16 - 6. Method according to any of claims 1 to 5, wherein determining a bearing condition on the basis of the bearing temperature and the second temperature includes: providing a predetermined look-up table to indicate the bearing condition in dependence on the bearing temperature and the second temperature.
7. Method according to any of claims 1 to 6, wherein determining a bearing condition on the basis of the bearing temperature and the second temperature includes: providing a correlation algorithm or correlation function, wherein by the correlation algorithm or correlation function the bearing temperature and the second temperature are correlated with the bearing condition.
8. Method according to any of claims 1 to 7, wherein further an operation parameter is detected, wherein for determining the bearing condition the operation parameter is included.
9. Method according to claim 8, wherein the operation parameter is one or more of a power consumption, a rotational speed and an acceleration rate of the vacuum pump.
10. Method according to any of claims 1 to 9, wherein a bearing failure is determined when the bearing temperature increases while the second temperature is substantially constant and in particular the rotational speed of the rotor constant.
11. Method according to any of claims 1 to 10, wherein no bearing failure is determined when the bearing temperature increases while the second temperature increases wherein the increase of the bearing temperature is -17 -larger than the increase of the second temperature and in particular the rotational speed of the rotor increases or has recently increased.
12. Method according to any of claims 1 to 11, wherein no bearing failure is determined when the bearing temperature is substantially constant while the second temperature increases and in particular the rotational speed of the rotor is substantially constant.
13. Method according to any of claims 1 to 12, wherein no threshold is defined for the absolute values of the bearing temperature and preferably no threshold is defined for the absolute values of the second temperature.
14. Vacuum pump comprising a housing, a rotor assembly disposed in the housing and supported by two bearings, wherein at least one bearing is a roller bearing, wherein a first temperature sensor is arranged at the at least one roller bearing to detect the bearing temperature and a second temperature sensor arranged at the vacuum pump, wherein the first temperature sensor and the second temperature sensor are connected to a control unit, wherein the control unit is configured to perform the steps of the method according to any of claims 1 to 13.